Variable transformer structure



R. SCHARLI 1,915,168

June 20, 1933.

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Patented June 20, 1933 UNITED STATES PATENT oar-lea :avnou' serum, or mmnn, swnznanann, ASBIGNOB 'ro axrmansmscnnr renown, novnax at out, or namm, swrrznmmo, A JOINT-STOCK OOIPAKY, or

' SWITZERLAND VARIABLE TRANSFORMER STRUCTURE Application filed March 81, 1981, Serial No. 526,815, and in Germany April 14, 1980.

This invention relates to im rovements in transformers such as sin le p ase transformers which are require to deliver a heav load at a widely variable voltage.

When a single phase supply of power is used as is frequently the case in electric traction systems, the traction motors are supplied through a transformer which must be ca able of delivering the high currents required at the widely variable voltages which are best suited for eflicient operation of the motorsl The arrangement of taps on the transformer secondary windin is impractical and undesirable due to t e high currents to be handled. Regulation of the secondary or output voltage by the addition of other windings is likewise practically impossible due to the extensive range required in regulation. The use of auto-transformers between the supply line and the supply transformer has also been proposed but such use is unsatisfactory due to the. increased weight and the space requirements which can be met only with great difliculty-and frequently decrease the effectiveness of the loco- It is, therefore, among the objects of the resent invention to provide a unitary transormer structure, particularly for traction urposes, which ma be regulated to deliver igh current at wi ely variable voltages.

Another object'of the invention is to provide a single phase transformer structure which will be capable of supplying high currents at the different voltages most effective for the operation of traction motors under different conditions.

Another object of the invention is to provide a combined auto-transformer and supply transformer structure in which the autotransformer is tapped to permit voltage regulation and to permit the supply of high current on the secondary side of the structure.

Another object of the invention is to pro vide a combined auto-transformer and supply transformer structure in which a two-legged core is provided with three yokes and the several windings are distributed over the two legs. Another object of the invention is to provide a combined auto-transformer and sup Objects and advantages, other than those above set forth, will be apparent from the following description when read in connection with the accompanying drawing which somewhat diagrammatically illustrates one embodiment of the present invention.

Referring more particularly to the draw-' ing by characters of reference, the reference numerals 1 and 2 designate the two legs of a transformer core which legs are connected by three yokes 4, 5 and 6. An auto-transformer is shown as being divided into two windings 8. 9 shown for the purpose of clearness as being'arranged on the core legs 1., 2 at one side of the middle yoke 5. It will be understood that the winding 8, 9 may beinterleaved in the actual arrangement thereof to diminish the reactance effect of the windings. The windings 8 and 9 of the auto-transformer are connected with the input line 11 and are tapped so that the output or secondary voltage may be varied by operation of a tap changer 12. It will be seen that, regardless of the direction of movement of the tap changer, voltage of line 11 is applied to a constant number of turns of winding 8, 9 thereby maintaining the voltage per turn of the winding constant and that the sum of the number of effective turns of the winding 8, 9 will always remain the same.

A transformer formed with a plurality of windings 13, 14 and 16, 17, distributed on the two legs of thecore on the side of the middle yoke 5 opposite to that occu ied by the autotransformer, is soarrange that the windings 13, 14 form the primary and the wind ings 16, 17 form the secondary windings of the transformer. It will be understood that the windings may be connected either in series or in parallel dependent on the operating characteristics desired for the transformer. The primary winding 13, 14 is connected with the auto-transformer 8, 9 by means of the tap switch 12 and is connected with the one terminal of an output line 19 actually forming an extension of one side of the line 11 which may be grounded if desired. The secondary winding 16, 17 is shown as being connected in parallel and as connected with the terminal of the line 19 already mentioned. The other terminal of line 19 is connected between the portions 16, 17 forming the secondery winding.

The middle yoke 5 thus has the momentary diiierence of the magnetic fluxes of the two transformers flowing therethrough and the number of turns of the auto-transformer are so determined that the average difference of the fluxes in the middle yoke is a minimum. The construction disclosed has the advantage over structures now known and used for similar purposes of a great decrease in weight with greater freedom in spacing of the windings as well as in being simpler in construction and therefore less expensive to construct.

Although but one embodiment of the present invention has been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

The invention claimed is:

1. In a transformer structure, a core of magnetic material, a primary winding distributed on the legs of said core, the several coils of said winding being tapped, a tap switch connecting the several coils of said primary winding, said tap switch being operable in such manner that the total number of effective turns of said primary winding remain the same regardless of operation of said switch, a second primary winding distributed on the legs of said core and being conductively connected with said tap switch, and a secondary winding distributed on the legs of said core.

2. In a transformer structure, a core of magnetic material having two legs joined by a pair of end yokes and an intermediate yoke, a primary winding distributed on the legs of said core on one side of said intermediate yoke, the several coils of said winding being tapped, a tap switch connecting the several coils of said primary winding, a second primary winding distributed on the legs of said core on the side of said intermediate yoke opposite to the said one side thereof and being conductively connected with said tap switch, and a secondarywinding distributed on the legs of said core on the same side of said intermediate yoke as the said second primary winding, the said intermediate yoke forming a closed circuit path for the difierence of magnetic flux between the first said primary winding and the combined flux of the second said primary winding and said secondary winding.

3. In a transformer structure, a core of magnetic material having two legs joined by a pair of end yokes and an intermediate yoke, a primary winding distributed on the legs of said core on one side of said intermediate yokes, the several coils of said winding being tapped, a tap switch connecting the several coils of said primary winding, a second primary winding distributed on the legs of said core on the side of said intermediate yoke opposite to the said one side thereof and being conductively connected with said tap switch, and a secondary winding distributed on the legs of said core on the same side of said intermediate yoke as the said second primary winding, the said intermediate yoke forming a closed circuit path for the diiference of magnetic flux linking with the first said primary winding and the magnetic flux linking with the second said primary Winding and said secondary winding, the connection of the coils of the first said primary winding by said tap switch being such as to reduce the diiference of magnetic flux in the said intermediate yoke to a minimum.

4. In a transformer structure, a unitary magnetic circuit, an auto-transformer winding divided into sections arranged about one part of said circuit, the said winding being provided with line terminals and the respective sections thereof having variable voltage taps, switch means cooperating with said taps for complementarily increasing and decreasing the eifective number of turns of the respective said sections, and multiple circuit transformer windings arranged about another part of said magnetic circuit, one of said multiple circuit windings having one end thereof connected to one of said line terminals and the other end connected with said switch means whereby the effective turns of said auto-transformer winding is maintained constant and the said one of said multiple circuit windings may be energized at full line potential, or any desirable lower po ential.

In testimony whereof I have hereunto subscribed my name this 18th day of March RUDOLF SCHARLI. 

